Officials say reports of an active shooter at a military post outside Washington stemmed from someone who made a distress call Thursday after seeing security forces doing a routine inspection.

The confusion was heightened by a planned active shooter drill at Joint Base Andrews that had not yet begun and was planned for later in the morning. Officials said in a Facebook post Thursday that there was no shooter and no threat to the base or workers there.

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The base had been placed on lockdown about 9 a.m. after an active shooter was reported. The base is home to Air Force One and is about 20 miles from Washington.

About an hour and a half later, the military post tweeted that the lock down had been lifted, except for the medical building where the active shooter was reported.

A law enforcement official said no active shooter was found at the post.

The law enforcement official was not authorized to discuss the matter by name and spoke on condition of anonymity.

"Fortunately, this was not a life-threatening situation," Col. Brad Hoagland, 11th Wing and base commander, said in the Facebook posting. "We take all threats seriously and reacted to ensure the security of those on the base."Vice President Joe Biden was scheduled to leave from Andrews on Thursday morning, but his trip was delayed by the lockdown.

The vice president's office said he was waiting out the delay at his residence at the Naval Observatory in Washington.

Biden was due in Columbus, Ohio, for a midday campaign event for former Gov. Ted Strickland, who is running for Senate.

The president, vice president and other senior government officials fly in and out of Joint Base Andrews.

President Barack Obama was last at the base Wednesday night when he returned from a trip to Ottawa, Canada

Emergency vehicles in the area of the base had on lights Thursday, but no sirens. At least three people in camouflage and helmets could be seen walking working dogs around the three-story building. About 10:15 a.m., a few people could be seen walking out of the building, including a person being moved in a wheelchair.

Rodney Smith, the patient advocate at the Andrews medical facility, said an active-shooter exercise was scheduled for Thursday morning, and then he was told it was a "real-world" situation.

"First it was an active-shooter exercise. Then it came back 'real world,'" Smith said by phone Thursday morning.

Smith said the situation was unfolding at the newer of two buildings at the Malcolm Grow Medical Facility. He was in the older building.